Voice-operated relay circuits



May'l7, 1932. B. G. BJRNsoN 1,859,019

VOICE OPERATED RELAY cRcUITs Filed Sept. 12, 1930 3 Shee'css-Sheerl l jimi /NVE/ v Tol? 5.6. BJRNSON ATTORNEY May 17, 1932. V B. G. BJRNSON VOICE OPERATED RELAY CIRCUITS Filed sept. 12, 193C. s sneetshet 2 /N VEN TOR B. G BJORNSON A TTORNEV May 17, 1932- B, G. BJRNsoN 1,859,019

VOICE OPERATED RELAY CIRCUITS Filed sept. 12. 1930 s sheets-sheet s Arrow/EY Patented May 17, 1932 BJan G. Mortensen, or NEW YORK, n. Y.,

VPATENT 'ori-lcs- ASSIGNOR TO BELL TELEPHONE LABORA- TORIES, INCORPORATED, VO1? NEW'YORK, N. Y., A CORPORATION 0F YORK VOICE-OPERATED RELAY CIRCUITS Application `filed September 12, 1930. Serial No. 481,363.

lcuits and the like.

@ne of the difficulties encountered in the yproper operations of such circuits is that steady alternating currents such as those set up in the telephone-circuits by induction from power linesand other adjacent circuits and other random noises are a serious limitation on the sensitivity at which a voice-operated circuit, such as an echo suppressor, can be worked. 'This diiiiculty is a serious one since the sensitivity of an echo suppressor is lim,-

ited by the noisiest circuit which may be con- `currents even though the voice currents be of the same order of magnitude as compared to the noise currents.

In the patent application of Robert C. Mathes, Serial No. 355,136, filed April 18, 1929, `a voice-operated relay circuit is disclosed which is rendered operative Yby the syllable frequencies and in which arl'l'frequencies above the syllable frequencies are suppressed, whether these 'frequencies are voice frequen- `cicslo'r noise frequencies ythat is, 'the circuit is rendered operative Aonly by such frequencies as are included yin the syllable frequency range. Y l

Another Aobject of the Vinvention is to provide means forfmaintainingthe device operated on sustained syllables.

A -feature of the invention is the use of an auxiliary relay 'in lthe plate circuit of the first detector which auxiliary relay operates when a sustained syllable of high amplitude is transmitted-throughthe device, which when operated, removes -a part of the grid bias of the second detector to maintain the device operated. y

Another object-of the invention is to provide means for operating the system von the initial part ofthe speech wave, lwhen the slope of the wave is small, and, at -the .same

time, permitting the system to release in a relatively short time after :the cessation of the speech wave. i

Another feature of the invention is the yuse 'of two syllabic detectors, an operating detector which loperates quickly to avoid initiale'lipping anda Iless sensitive or follow-up detector which operates sometime during the decay of the syllable, and which has a shorter time of release.

Another object ofthe invention :is to 'provide a voice operated circuit involving noise protection, based on speech frequency discrimination, vfundamental pitch frequency discribination, and syllabic frequency discrimination. i

Another feature yof the invention is the use of a iilter, or filters, which will pass currents in the pitch frequency range, i. e. .the fundamental frequency of the voice, to the :exclusion of other frequencies and a pitchdetector between the speech detector and the -l-ter which passes only sylllabic frequencies.

The invention is applicable to any kind of voice-operated systems, but hasspecia'l appli cation to those types Where linterference fromV external noises is troublesome.

Another object of the invention to pro vide means in a two-way communication system for .disabling the voice-operated syllabic relay-device when signals .are being received from the other direction. Y

Another object of the" invention is Ato :employ a vacuum tube as a relay to "block the transmission path.

The invention will be better understood by lreferring to the following `description and laccompanying drawings lin which Fig. l is a circuit diagram of a terminal .of a i-wire voice controlled circuit showing yone embodiment of the invention; and Figs. 2 and i3 :are similar showings of modified forms of lthe invention.

Referring to Fig. l, the line L `is shown terminating in a .hybrid coilschematically indicated at 10, and having a balancing .impedance il. An eastward vtransmitting branch 212 and .a westward transmitting branch :13

are associated with the hybrid coil 10. Amplifiers 14 and 16 and a delay network 15 are preferably associated with the eastward transmitting branch 12. Amplifiers 17 and 18 and a delay network 19 are preferably associated with the westward transmitting or receiving branch 13.

The eastward or transmitting branch 12 is normally disabled by the normally closed switch 20. The switch 2O is controlled by the relay 21. The westward or receiving branch 13 is normally in an operative condition. This branch is arranged to be disabled by the opening of the normally closed switch 22 under control of the relay 23.

The input circuit 24 of a voice operated equipment is bridged across the eastward or transmitting branch 12 between the amplifier 14 and the delay network 15. The voice operated equipment comprises the circuit 25, which is tuned to a frequency of approximately 1200 cycles per second, an amplifier 26 which is coupled to the tuned circuit by means of a transformer 27, a speech detector 28 which is coupled to the amplifier 26 by means of a Atransformer 29, a 75-315 cycle band-pass filter 30 which is coupled to the speech detector 28 by means of a transformer 32, a pitch detector 31 associated with the filter 30, a low pass filter 33 which is coupled to the pitch detector 31 by means of a transformer 34, a syllabic operate detector 35 and a syllabic follow-up detector 36 which are connected to the low-pass filter 33, and a re- "lay 37.

The filter 30 may be of the type well known in the art, for example, as disclosed in S.

VPatent to Campbell Nos. 1,227,113 and 1,227

114, granted May 22, 1917. Y

The pitch detector 31 may be of the type well known in the art, for example, it may be similar to the speech detector 28. Preferably however the pitch detector 31 with the associated transformer 34 is of the type disclosed in the patent application of R. C. Mathes,

Serial No. 356,136, referred to above, and shown on D of the Mathes drawing, to provide for a cut-off at approximately two cycles.

The filter 33 is of the low-pass type having preferably a cut-ofi:l at or near the maximum syllable frequency which is in the neighborhood of twenty-ve cycles.

An auxiliary relay has its winding connected in the plate circuit of the detector 28.

" It is preferably connected between the plate battery 110 and the primary winding of the transformer 32, as shown, so as to serve as a choke coil in addition to its function as a relay. A switch 61 is closed by the operation of relay 60, and when closed, it short-circuits the battery 62 and resistance 63 which are connected in the grid circuit of the syllabic operate detector 35.

A voice operated echo suppressor circuit f has its input circuit 41 bridged across the westward or receiving branch 13 between the amplifier 17 and the delay network 19. The echo suppressor circuit comprises a tuned circuit 42, an amplifier 43, a detector 44, a relay 45, the winding of which is in the plate circuit of the detector tube 44 and a relay 51, the operation of which prevents the voice operated equipment connected to the eastward branch 12 from disabling the westward or receiving branch 13. The relay 51 is pro'- vided with a winding 57 which is associated with a battery 56, resistances 58 and 59 and condenser 55 to provide a time lag in the release of the relay 51.

The operation of the circuit is as follows: (It being understood that speech arriving from the line L is to open up a path for itself by opening the switch 20, while noise current on the line will be prevented from opening the switch 20.) Part of the voice currents over the eastward or transmitting branch 12, in the direction indicated, pass through the delay network 15 and amplifier 16 and part of them are shunted from the eastward or transmitting branch 12 to the input circuit 24 of the tuned circuit 25. As this tuned circuit 2'5 is tuned to a frequency of approximately 1200 cycles it will pass only frequencies in this neighborhood (a frequency band in which the speech energy is large with respect to the noise energy). Voice current in this frequency band will pass from the tuned circuit 25 through the transformer 27 to the amplifier 26 and through the transformer 29 to the speech detector 28.

The detected current is impressed on the filter 30 by means of a transformer 32. The filter 30 passes to the detector 31 only currents in the frequency band between and 315 cycles. It has been determined experimentally that the pitch frequency (or thc fundamental frequency) of the voice lies within the frequency band from 75 to 315 cycles. The pitch frequency currents are detected by the detector 31.

The detected currents are transmitted to the filter 33 by means of the transformer 34. The filter 33 preferably passes enly currents below 25 cycles and the transformer 34 preferably has a lower cut-off at approximately 2 cycles. Currents within the frequency band from 2 to 25 cycles are impressed on the input circuit of the syllabic detectors 35 and 36. The output currents from the syllabic detectors 35 and 36 operate the relay 37.

The operation of relay 37 opens the switch 38 allowing suflicient current from the source of potential 39 to flow through the windings of relays 21 and 23 and operate the correspending associated switches 20 and 22. The

opening of switch 2O removes the short-circuit from across the eastward or transmitting branch 12, allowing the voice currents from the line L to be transmitted over the eastward or transmitting branch. The opening of llO 'SIG

thespeechfsyllables and the follow-up detector 36 is less sensitive than the operate 'detector 35, since it has only to operate sometime during the decay of a syllable. vThis adjustment is `preferably made by regulatingthe negative grid bias on the detectors Aand 36. l/Jith the syllabic detectors 35 and 36 biased in this manner it has been found possible to obtain a much shorter releasing time after the end of a syllable, for the relay 37, Athan when the detectors 35 and 36 are of equal sensitivity.

' ing point Vof the speech detector. As long as the switch 61 is maintainedin `a closed position by the auxiliary 'relay 60, sufficient current will fiow in the plate circuit of the operate syllabic detector 35 through the relay -37 =to maintain the .relay 37 operated. In this manner the relay 37 is maintained operated on high level steady impulses.

Speech currents arriving from the east Vover receiving branch 13 through the amplifier 17 are transmitted in part through the delay network 19, amplifier 18 to the line L,.and in part over the path 41 through the tuned circuit 42, amplifier 43 and detector 44, thereby operating the relay 45. When the relay 45 operates the switch 46 removes the ground from the contact 48 and puts a ground on the contact 47. When ground is removed from the contact 48 vsufficient current flows from the source of potential 49 through the winding 50 on relay 51 to op- -erate the relay 51. When therelay 51 operates it `disconnects the switch 52 from the ,contact I53 and connects the switch 52 with the contact 54, thereby placing a short-circuit across the secondary winding of the transformer 34 and opening Vthe circuit between the transformer 34 and the grid potential battery 62 of the syllabic operate-detector 35. This prevents either noise or voice currents from the eastward or transmitting branch from causing the operation of relay 37, which relayv if operated would open the switch 38 `and cause the westward or receiving branch to be disabled.

rlhe blocking of the transmitting control circuit `at the output of the low 1pass filter 33, by the opening of the contact 53, will allow the use of a delay circuit 19 having shorter delay characteristics than those employed in the prior-art, and in some cases will allow the omission .ofthe delajyfeircuit `19.,fsince:th'e time delay in the low pass filter E33 will prevent echocurrents from fthe :receiving branch from operating .thezrclay 37 before the relay :51 of the receiving -control circuit fhas operated.

The shorting of Athe input side `of the filter -3-3 by the closing of contact 53 prevents the storage of an excessive amount 1of energy in the filter 33. If the echo currents were :permitted to store up an excessive lamount :of energy in the filter 33 itV would :be necessary to provide `a large hangover in the receiving branch control circuit Yto `avoid false operation of relay 37 by the energy stored up in the filter 33 after the relay 51 releases.

At the cessation of the Vspeech impulses from the westward or receiving branch 1'3 the relay 45 will release, causing theswitch 46 to disconnect from the contact 47 and connect with the vContact 48. When 'the switch 46 makes connection with the contact 148, .the condenser 55, which has previously ldischargedthrough the resistance 59, contact 47 and switch 46, is charged by the battery 56, through the winding 57 and `resistance 58. (The discharge of the condenser v through the resistance 59, contact 47 and switch 46 to ground took place when the relay .45 was in its operated position.) rlhe charging of condenser 55 as described Aholds the relay 51 operated while the condenser 55 is being charged and prevents `either voice or `noise currents on the eastward or `transmitting branch 12 from ldisabling the westward 0r receiving branch 13 immediately after the relay 45 has released upon the cessation of a syllable, thereby maintaining the westward or receiving branch loperated for Vthe succeeding syllable.

When desirable the filter 30, which 'passesv a `band of frequencies between 75 and -315 cycles, and the pitch detector 31' may be omitted, Vin rwhich case the speech detector 28 would be coupledto lthe low-,pass vfilter y33 by means of a transformer, such as the zt'ransformer 34.

Fig. 2 illustrates a voice operated terminal circuit similar to that shown in Fig. 1. A band-pass filter 65 is connected Ito :the eastward or transmitting branch =12=throughthe path 24. This filter '65 is designed to pass vonly frequencies `Vwithin the voice vrange inv frequencies between 2 and 2O cycles.

and the detector 28 coupled directly to the band-pass filter 65.

A series of band-pass filters 66, 67, 68 and 69 are connected in parallel to the output of the speech detector 28. These filters are de- -signed to divide the detected speech currents into four equal frequency bands. In the particular noise protection circuit illustrated the filters were designed to pass the following frequencies and to substantially exclude other frequencies:

Filter No. 66-75 to 135 cycles; Filter No. 67--135 to 195 cycles; Filter No. 68--195 to 255 cycles; Filter No. 69-255 to 315 cycles. These filters may be of the type well known in the art for example, they may be designed in accordance with the disclosure published inthe Bell System Technical Journal, January 1925, vol. 4, No. 1, entitled Mutual inductance in wave filters with an introduction on filter design by K. S. Johnson and T'. E. Shea.

Individual pitch detectors 31 are connected to the output of each of the filters 66, 67 68 and 69.

Individual filters 70 are connected to the output of each of the pitch detectors 31. These filters are preferably designed to pass They may be of any type well known in the art. For example, they may be designed in accordance with the disclosure published in the Bell System Technical Journal referred to above.

Individual syllabic detectors 74 are connected to the out-put of the filters 70. These syllabic detectors are preferably of the type shown in F 1 comprising the detectors 35 and 36. Individual relays 7 8, 79, 8O and 81 are connected to the output circuit of the syllabio detectors 74. Normally closed switches 82, 83, 84 and 85 are associated with the relays 78, 79, 80 and 81 respectively. The operationv of the relays 78 to 81 inclusive opens the respective switches 82 to 85 inclusive.

The switch 61, which is actuated by the relay 60, is shown connected to the syllabic detector 74, which is associated with band-pass filter 69, although it might as well be associated with any of the other three syllabic detectors 74. A receiving control circuit 114, the same as the control circuit 114 shown in Fig. 1 is connected to the receiving branch 13 to control the operation of relay 51. A normally closed switch 115, which is associated with the relay 51 is connected in battery supply lead 116 of the battery 39.

The operation of this system is as follows: The voice frequency currents passing through the band-pass filter 65 are detected by the detector 28. The detected currents from the detector 28 pass through the filters 66, 67, 68 and 69. Currents within the frequency bands from 7 5 to 135 cycles will pass through the filter 66, be detected by the pitch detector 31 associated therewith, and the detected currents in the frequency band from 2 to 2O cycles will pass through the filter 70, be detected by the syllabic detector 7 4 and actuate the relay 78.

Similarly currents from the output of detector 28 within the frequency band from 135 to 195 cycles will cause the operation of relay 79, currents within the band from 195 to 255 cycles will cause the operation of relay 80, and currents within the band from 255 to 315 cycles will cause the operation of relay 81.

The operation of any one of the relays 78 to 81 inclusive will open the corresponding associated switches 82 to 85 inclusive. Since the switches 82 to 85 inclusive are connected in series the opening of any one of them will remove the short circuit from the source of potential 39 and its associated resistance and allow sufficient current to flow through the relays 21 and 23 to open the switches 20 and 22.

Since the pitch frequencies of the voice vary from about 90 cycles to about 300 cycles and since the fundamental pitch will vary but little during the utterance of a syllable, most of the energy of individual syllables in the output of the speech detector 28 will be llocated in a unique narrow frequency band somewhere between 90 and 300 cycles, and as the frequency band from to 315 cycles has been divided into four parts by means of the filters 66 to 69 inclusive, noise energy having a uniform spectrum is divided into four parts, thereby decreasing` the sensitivity of the circuit for noise currents. This is due to the fact that, at a given instant of time, most of the speech energy will reach one of the relays 78 to 81 inclusive, while only one-fourth of the noise energy having a uniform spectrum will reach that same relay, and the -operation of any one of these relays will cause the operation of relays 21 and 23.

If desirable, the frequency bands of the filters 66 to 69 inclusive can be made to overlap slightly so as to provide better transmission for the fundamental voice frequencies falling near the filter cut-offs.

The receiving control circuit 114 functions in a similar manner to the control circuit shown in Fig. 1, except that the switch 115 opens the battery supply lead 116, thereby preventing the operation of relays 21 and 23 when relay 51 is operated.

The system shown in Fig. 3 is similar in general to that shown in Fig. 1. A bandpass filter 65, the same as the filter 65 shown in Fig. 2 is employed in place of the tuned circuit 25 of Fig. 1. A detector 90 is coupled to the amplifier 26 by means of the transformer 29. The detector circuit illustrated is of the grid-condenser-resistance or grid current type insteadi of the-plate circuit type illustrated in Fig. 1.

The grid current type of detector has two advantagesover the plate circuit type of' detector. It is more efficient than the plate cirofV detector, in which the output level of the difference frequency changes by twice the amount of the'- chan-ge in. the input level, dine to its parabolic plate circuit characteristic.v

W'ith'a plate circuit type of detector it is necessary toemploy a low-pass filter such as the filter 33 in Fig. 1, which has attenuation characteristics twice as great as when the attenuation for the diflerence frequency is;

and is coupled to the detector v90 by meansofthe transformer 92 instead of the low-pass filter 33 of Fig. 1 of the mid shunt type.

The primary winding of a transformer 102 is shunted across the output of the low-pass filter 91. The input circuit of the vacuum tube 93 is connected to the secondary winding ofthe transformer 102. A source of po-. tential 94, a resistance 95, shunted by a condenser 96, and a switch 97 are connected in series in the output circuit of the vacuum tube 93. The switch 97 which is normally closed, is opened by theoperationof a relay 98, the winding of which is connected in shunt to the windingof the relay 37.

The ampl-ier 16 of Fig. 1 Ahas been replaced by a push-pull amplifier employingtubes 99 andv 100, the input circuits of which are associated with the output circuit of the delay network 15 by means of a transformer 101. The source of potential 103 and the resistance 95, in shuntwith the condenser 96, are connected in series in the input circuit of the vacuum tubes 99 and 100 to provide grid biasing potential therefor.

' rlhe auxiliary relay 60, which actuates the switch 61, has its winding connected in the plate circuit-'of the detector 90 in a similar manner to that shown in Fig. 1 in connection with the detector 28.

The operation ofthe system is as follows: Speech currents coming from the line L are amplified by the amplifier 14 and part of-,them are shunted to the input of the filter 65. The

, currents between the frequencies of 800 and 2000 cycles pass from the filter 65 through the amplifier 26 to the input-of the detector 90. The detected currents are transmitted through the transformer 92 to the low-pass filter 91, which has a cut-ofil at approximately 25 cycles. These currents are detected by the syllabic detectors 35 and? 36. The detected currents from the output of detectors 35 and 36 actuatethe relays-37 and 98. Part of the currents from the output of the lterV 91 are transmit-ted th-roughthe transformer 102 to the input circuit of the vacuum tube 93.

The currents impressed onthe input circuit of the vacuum tube 93 reduce the amount of plate current flowing inthe output circuit of the vacuum tube- 93. A reduction in the plate current fiowing through the resistance 95 reduces the amount of negative bias on the. tubes 99` and 100 thereby putting the tubes 99 and 100v in an. operative condition. After the plate current through the tube 93 has been reduced sufficiently to render the amplifier tubes 9-9 and 100- operative, the relay 98 opera-tes and opens the switch 97. This insures that the amplifier tubes- 99A and 100V will re` mai-n in an operatedcondition as longas theV relay 98 remains operated. v

At the cessation of the signal currents through the filter 91 and the syllabic detec tors 35 and 36the relay 98l will release, causing the switch 97 to close. Thijsial'lows'normal plate current to again flow in the tube 93, thereby rendering the amplifier tubes 99 and 100 inoperative.

Relays 37 and 23 function in the same manner asV the' corresponding relays i-n Fig. 1, thereby rendering the eastward or receiving branch 13 operative and inoperative.

The switch 61, which is actuated by the auxiliary relay 6 0, functions in the same manT ner as described above in connection with the circuit shown in Fig. 1, to maintain the relays 37 andv 98 operated when the currenty level through the speech detector 90 is high.

The echo'suppressor circuit comprising the path 41, filter 105,amplifier 43, detector 44,

and relays 45 and 51 function in the same manner as the echo suppressor circuit shown in Fig. 1 exceptl that'the relay 51 opens a normally closed switch 106 which disables the voice operated circuit connected to the eastward branch 12 by opening the circuit be-r tween the transformer 92 and the condenser 104 of the filter 91.

While but certain embodiments of the invention have been shown and described in detail it is understood that the invention is generic in character and is not tobe'considered as limited to the particular embodiments described since'numerousl modifications thereof may be made without departing from the spirit of applicants invention, the scope of which is to be determined by the appended claims.-

What is claimed is: j 1. In a voice-operated relay'circuit, a path over which voice frequency currents and rela-KVV tively sustained alternating currents may be transmitted, tandemdetectors associated withsaid path, a relaycontrolledby the second detector, means rendering said second detector selectively responsive to syllable frequency currents, and means associated with said first detector for rendering said relay operative in response to sustained voice frequency currents having a high level.

2. In a voice-operated relay circuit, a path over which fluctuating voice frequency currents and relatively sustained alternating currents may be transmitted, a detector associated with said path, means associated with said detector for transmitting a selected band of frequencies, other detectors having sensitivity characteristics which differ from each other connected to said last mentioned means, and a relay controlled by said other detectors.

3. In a voice-operated relay circuit, a path over which voice frequency currents and relatively sustained alternating currents may be transmitted, tandem detectors associated with said path, a relay controlled by the second detector, means rendering said second detector selectively responsive to syllable frequency currents, and means for rendering said voice-operated relay circuit inoperative while maintaining said first detector in an operative condition. Y

4. In a voice-operated relay circuit, a path over which fluctuating voice frequency currents and relatively sustained alterating currents may be transmitted, a detector associated with said path, means associated with said detector for transmitting a selected band of frequencies, other detectors having sensitivity characteristics which differ from each other connected to said last mentioned means, a relay controlled by said other detectors, and means for rendering said voiceoperated p relay device inoperative while maintaining said first mentioned detector in an operative condition. v

5. In a voice-operated relay circuit, a path over which voice frequency currents and relatively sustained alternating currents may be transmitted, tandem detectors associated with said path, a relay controlled by the second detector, means rendering said second detector selectively responsive to syllable frequency currents, and means for rendering said voice-operated relay circuit inoperative, said last mentioned means blocking said circuit between said first detector and said means for rendering said second detector selectively responsive to syllabic frequency currents.

6. In a voice-operated relay circuit, a path over which fluctuating voice frequency currents and relatively sustained alternating currents may be transmitted, a detector associated with said path, means associated with said detector for transmitting a selected band of frequencies, other detectorshaving sensitivity characteristics which diifer from each other connected to said last-mentioned means, a relay controlled by said other detectors, and

currents, a detector associated with said last mentioned means, a relay controlled by said detector, and means to substantially prevent the effect of currents other than currents of syllable frequency from being transmitted to said detector.

8. In a voice operated relay circuit, a path over which fluctuating voice currents and relatively sustained alternating currents may be transmitted, a detector associated with said path, a second detector associated with said path, means connected between said rst.

mentioned detector and said second detector to substantially prevent the effect of currents other than currents of pitch frequency from being transmitted from said first mentioned detector to said second detector, a third detector associated with said path, means connecting said second and third detectors to substantially prevent the eect of currents other than currents of syllable frequency from being transmitted to said third detector, and a relay controlled by said third detector. 9. In a voice operated relay circuit, a path over which fluctuating voice currents and relatively sustained alternating currents may be transmitted, a detector associated with said path, a plurality of means associated with said detector for transmitting different frequency bands, all of said different frequencyrbands being within the fundamental or pitch frequency voice range, other detectors connected to said last mentioned means, means associated with said last mentioned detectors for substantially preventing the eect of currents other than currents of syllable frequency from being transmitted therethrough, other detectors connected to said last mentioned means, and relays controlled by said last mentioned detectors, said relays having their contacts connected in series.

- `10. In a four-wire voice controlled circuit, a path over which voice frequency currents may be transmitted, means including a low pass iilter, a detector and a relay associated with said path for rendering said path operative, said detector having its input circuit connected to the output circuit of said low pass filter, a second path over which voice currents may be transmitted, means including a second detector and a second relay associated with said second path for preventing said' BJRN G. BJRNSON. 

